Our recent study on the nature of magnetic domain walls in ultrathin ferromagnetic films has just appeared in Nature Communications.
In ultrathin ferromagnetic films with perpendicular anisotropy, such as Ta/CoFeB (1 nm)/MgO and Pt/Co (0.6 nm)/AlOx, it has been suggested that the presence of an interfacial chiral interaction of the Dzyaloshinskii-Moriya form, arising from the strong spin-orbit interaction in the “heavy metal” underlayer (Ta, Pt), could have a significant impact on the spin structure of the domain walls in such films. In particular, a sufficiently strong Dzyaloshinskii-Moriya interaction can favour Néel domain wall states over the Bloch states expected for such films. By using a novel scanning magnetometry method based on a single nitrogen-vacancy defect in a diamond nanocrystal, my colleagues at the Laboratoire Aimé Cotton in Orsay have shown unequivocally that the Dzyaloshinskii-Moriya interaction is large enough to promote Néel walls in Pt/Co (0.6 nm)/AlOx, while no signature of this interaction is present in Ta/CoFeB (1 nm)/MgO.
This finding has some important consequences on possible applications involving magnetic domain walls, such as racetrack memories, since current-driven spin torques like the spin Hall effect influence Bloch and Néel walls differently. Moreover, the presence of a strong Dzyaloshinskii-Moriya interaction in Pt/Co (0.6 nm)/AlOx suggests that such material structures could be promising for harbouring exotic chiral spin structures such as skyrmions.